The present invention relates to boxes with layered or sandwich wall construction, especially those which must withstand severe torsion forces.
The layered walls in construction of boxes is useful in that lighter and less expensive materials may be used as a fill material between two rigid sheets. It is well known to use polymer foam material such as styrofoam or other rigid foams between two rigid polymer sheets to form a sheet of exceptional lightness, insurability and strength. However, the desired features of such a sandwich wall or sheet are not easily obtained.
While an unassociated sandwich sheet is very strong, excessive flexing, shock or vibration causes the rigid sheets to delaminate from their bonded connection to the Styrofoam. This delamination essentially destroys a major part of the wall strength. Subsequent blows or strikes against a delaminated sheet causes the force of the blow or strike to be focused on a small area instead of being distributed over the entire sheet. The rigid polymer foam is then compressed or broken into fragments, causing delamination of the polymer sheet on the other side of the sandwich wall. When such sandwich walls are used in box construction, bonded connections between individual wall pieces becomes difficult to achieve while ensuring precise orientation of all the other pieces in the box. Failure to obtain such precise orientation results in a box that will fail.
U.S. Pat. No. 4,744,445 describes components and methods for assembling storage cases. Storage cases are made for a wide variety of applications including transportation, shipping and storage and are required in a wide variety of shapes and sizes. The '445 patent describes a kit for assembling a case having a base and a lid from a series of separate parts is provided, the kit allowing cases of any chosen dimensions to be made. The assembly kit was described as a series of panels of any chosen dimensions for forming the bottom, side and end walls of an open topped box-like enclosure base, and similar panels for forming a lid for closing the open top of the base, a series of angled corner strips for connecting adjacent edges of the panels together along the longitudinal and side edges of the base and lid to form the box-like enclosures, a hinge mechanism for hinging the lid to the base, and a latch mechanism for releasably closing the lid. The kit also included mateable or co-operable edge strips for securing around the open upper end of the base and lower edge of the lid, respectively, for mating engagement with one another when the lid is closed to restrict movement of the lid relative to the base. Also provided in the kit were corner pieces for securing at the lower four corners of the base and the upper four corners of the lid. Metable corner pieces were provided in the kit which are of similar configuration to the mateable edge strips for securing to the upper and lower corner edges, respectively, of the base and lid. The disclosure U.S. Pat. No. 4,744,445 is incorporated herein.
Although useful for careful hobbyists, the kit of the '445 patent was the subject of many product returns. A single mis-aligned connection among the several bonded (i.e., via glue, thermal welding or other such polymer bonding methods) connections that were needed to make the case would result in a useless collection of pieces. So many returns were experienced that actual construction of the cases according to the '445 patent was performed by Melmat, Inc. in Huntington Beach, Calif., a company experienced in manufacturing and assembly of plastic devices. Although the cases described in the '445 patent can with care be assembled by professionals, it would be desirable to reduce the manufacturing care requirements to reduce manufacturing time and cost.
The case according to the '445 patent is shown and described using wall material of a single layer. The thickness of the wall material is relatively thin. It has been found that the wall material of the case according to the '445 patent is relatively weak compared with boxes formed with sandwich walls. However, the '445 patent and the prior art fail to indicate how the case of the '445 patent could be change to accommodate sandwich wall construction. There is a need for a case having the reduced number of manufacturing components as that of the '445 patent while obtaining the benefits of sandwich wall construction.